1. Field of the Invention
The present invention relates to a light emitting element, a light emitting element array including of a plurality of light emitting elements, a backlight unit that receives light from such a light emitting element array, and a liquid crystal display provided with the backlight unit.
2. Description of the Related Art
A common thin liquid crystal display like the one in JP-A-2006-64733 is equipped with a side-light type backlight unit having a light guide plate and an LED array (light emitting element array) that shines light on the side edge of the light guide plate.
Such a backlight unit includes an LED array 101 (see FIG. 15, which will be described later) including a row of LEDs 102 shown in FIG. 13 and FIGS. 14A to 14C, for example (FIG. 14A is a plan view of FIG. 13, FIG. 14B is a sectional view taken on the line a-a′ of FIG. 14A, and FIG. 14C is a sectional view taken on the line b-b′ of FIG. 14A).
The presence of a plurality of LEDs 102 (light emitting elements) offers the advantage of an increase in the amount of light emergent from the backlight unit in proportion to the number of LEDs 102. This increased amount of light increases the brightness of a liquid crystal display panel which leads to an improvement in display quality.
However, in the LED 102 shown in FIG. 13 and FIGS. 14A to 14C, a light emitting chip 121 is enclosed with side walls 132 of a package (housing member) 123. Therefore, a portion of light emitted by the light emitting chip 121 is cut off by the side walls 132. The LED array 101 composed of these LEDs 102 arranged in a line suffers from the following problems as a result of the light being cut off by the side walls 132 of the package 123. The problems will be described by referring to a sectional view of FIG. 15 showing the LED array 101 and the light guide plate 151, as seen from the same cross-sectional direction as in FIG. 14B (in FIG. 15, for convenience' sake, hatching has been omitted).
As shown in FIG. 15, if the space between the light exit surface of the LED 102 and the side edge of the light guide plate 151 is relatively narrow, the light emergent from the LED 102 reaches the side edge of the light guide plate 151 before it spreads across a relatively wide area (see arrow with solid line), and a portion of the light is cut off by the side walls 132 (see arrow with dashed-dotted line). Therefore, less light enters a portion of the side edge of the light guide plate 151 that opposes a space between the LEDs 102 of the LED 101 array (see the black colored portion in FIG. 15). As a result, the side edge of the light guide plate 151 (and hence the backlight unit) suffers variations in the amount of light present in the light guide plate 151, that is, while the portion opposing the LED 102 is relatively bright, the portion opposing the space between the LEDs 2 is relatively dark.
The following are two examples of the measures to address such a problem. Of these two measures, a first measure entails allowing the side edge of the light guide plate 151 to be nearly evenly supplied with light by widening the space between the LED 102 and the side edge of the light guide plate 151 such that the light from the LED 102 spreads across a somewhat wider area (at a wider angle). A second measure entails allowing the side edge of the light guide plate 151 to be nearly evenly supplied with light by a diverging light produced by the side edge of the light guide plate 151 that is carved into the shape of a lens.
However, adopting the first measure results in a reduction in entrance efficiency of light entering the light guide plate 151 due to a wider space between the light exit surface of the LED 102 and the side edge of the light guide plate 151. This leads to a reduction in brightness of the backlight unit. On the other hand, with respect to the second measure, there is a limit on the degree of divergence of light based on the lens shape. As a result, the second measure produces little effect if the space between the LEDs 2 of the LED array 101 is relatively wide. As described above, the first and second measures are not sufficient to eliminate the variations in the amount of light in the backlight unit.